I thought I had this one solved, based on a post I made in 2013. How-to-specify-a-default-layer

But I've run into problems trying to have one of a dozen layers come up as the default ... and then give way to another selection, based on the viewer's selection. I can make the layer display ... but it stays on the screen when other layers are selected. If I remove any special processing, the layer works fine, by itself. (Each layer is made up of text blocks that appear on top of a background image. My 2013 examples used images that overlaid one another ... so the entirety of the initial image was replaced.)

I named a mypopup1 element and then placed these lines in the body of the page:
<script type="text/javascript">
xr_v1(document.getElementById('mypopup1').parentNo de.parentNode)
</script>
Searching here and with Google, I haven't been able to find a shred of reference to either a default or initial layer (other than for my 2013 post).

Isn't there a more-or-less standard way to set one of the layers as an initial layer?

Thanks in advance for any help.